This invention relates in general to vehicle disc brake assemblies and in particular to an improved spindle nut assembly for an electric parking brake actuator for use in such a disc brake assembly.
Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies are actuated by hydraulic or pneumatic pressure generated when a driver of the vehicle depresses a brake pedal The structures of these drum brake assemblies and disc brake assemblies, as well as the actuators therefore, are well known in the art.
A typical disc brake assembly includes a brake disc or rotor which is secured to a wheel of the vehicle for rotation therewith. The disc brake assembly further includes a brake caliper that is slidably supported on pins secured to an anchor bracket. The anchor bracket is secured to a non-rotatable component of the vehicle, such as the axle flange or steering knuckle, which is connected to the vehicle frame. The brake caliper includes a pair of brake linings which are disposed on opposite sides of the brake disc. The brake linings are connected to one or more hydraulically or pneumatically actuated pistons for movement between a non-braking position and a braking position, wherein they are moved into frictional engagement with opposed braking surfaces of the brake disc. For example, when the driver of the vehicle depresses the brake pedal, the piston urges the brake linings from the non-braking position to the braking position so as to frictionally engage the opposed braking surfaces of the brake disc and thereby slow or stop rotation of the associated wheel of the vehicle.
The disc brake assembly may also include an actuator that is used to realize a parking brake function of the disc brake assembly. The actuator may be an electromechanical actuator. The actuator may comprise a rotationally restrained spindle nut threaded onto a motor driven spindle. As the spindle is rotationally driven, the spindle nut axially translates to move the piston and urge the brake linings between the braking and non-braking positions. The piston may be hollow with the spindle nut and spindle located inside the piston. When the brake linings are moved to the non-braking position, the spindle nut translates towards a stop surface of the spindle. Stops may be provided on the spindle nut and spindle such that a spindle nut stop engages a spindle stop before the spindle nut jams against the spindle.
However, when the spindle nut has multiple threads, the spindle nut is pre-positioned—e.g., a specific internal thread on the spindle nut is started on a specific external thread of the spindle—during assembly of the actuator such that the spindle nut stop will engage the spindle stop before the spindle nut jams against the spindle. Needing to pre-position the spindle nut increases assembly complexity fur the parking brake actuator. Therefore, it would be desirable to have the spindle nut stop engage the spindle stop without pre-positioning the spindle nut during assembly of the actuator.